A Self-tracked High-dielectric Wireless Power Transfer System for Neural Implants

This paper introduces a novel, efficient and long-range ( 0.5λ) wireless power transfer system for implantable neural devices. The operating principle of this system is based on the high-dielectric coupling, which occurs between an external lossless high-dielectric metamaterial (permittivity, ε r =100, loss tangent, tanδ = 0.0001) and lossy dielectric such as rat (ε r =54.1, conductivity, σ = 1.5 S/m). As magnetic field coupling occurs between two dielectric resonators, therefore, the rat (lossy dielectric) itself acts as a self-tracking energy source. The Ansoft HFSS simulation software was used to verify the concept. Initially, the rat was modelled as a phantom box and the resonant frequency was found to be 1.5 GHz. Then, for matching this intrinsic mode of the rat model, the external high-dielectric metamaterial designed accordingly to realize a highly efficient (η = 1×10 -3 ) and self-tracked wireless power system for neural implants

Beyond Tissue replacement: The Emerging role of smart implants in healthcare

Smart implants are increasingly used to treat various diseases, track patient status, and restore tissue and organ function. These devices support internal organs, actively stimulate nerves, and monitor essential functions. With continuous monitoring or stimulation, patient observation quality and subsequent treatment can be improved. Additionally, using biodegradable and entirely excreted implant materials eliminates the need for surgical removal, providing a patient-friendly solution. In this review, we classify smart implants and discuss the latest prototypes, materials, and technologies employed in their creation. Our focus lies in exploring medical devices beyond replacing an organ or tissue and incorporating new functionality through sensors and electronic circuits. We also examine the advantages, opportunities, and challenges of creating implantable devices that preserve all critical functions. By presenting an in-depth overview of the current state-of-the-art smart implants, we shed light on persistent issues and limitations while discussing potential avenues for future advancements in materials used for these devices

Improving the mechanistic study of neuromuscular diseases through the development of a fully wireless and implantable recording device

Neuromuscular diseases manifest by a handful of known phenotypes affecting the peripheral nerves, skeletal muscle fibers, and neuromuscular junction. Common signs of these diseases include demyelination, myasthenia, atrophy, and aberrant muscle activity—all of which may be tracked over time using one or more electrophysiological markers. Mice, which are the predominant mammalian model for most human diseases, have been used to study congenital neuromuscular diseases for decades. However, our understanding of the mechanisms underlying these pathologies is still incomplete. This is in part due to the lack of instrumentation available to easily collect longitudinal, in vivo electrophysiological activity from mice. There remains a need for a fully wireless, batteryless, and implantable recording system that can be adapted for a variety of electrophysiological measurements and also enable long-term, continuous data collection in very small animals. To meet this need a miniature, chronically implantable device has been developed that is capable of wirelessly coupling energy from electromagnetic fields while implanted within a body. This device can both record and trigger bioelectric events and may be chronically implanted in rodents as small as mice. This grants investigators the ability to continuously observe electrophysiological changes corresponding to disease progression in a single, freely behaving, untethered animal. The fully wireless closed-loop system is an adaptable solution for a range of long-term mechanistic and diagnostic studies in rodent disease models. Its high level of functionality, adjustable parameters, accessible building blocks, reprogrammable firmware, and modular electrode interface offer flexibility that is distinctive among fully implantable recording or stimulating devices. The key significance of this work is that it has generated novel instrumentation in the form of a fully implantable bioelectric recording device having a much higher level of functionality than any other fully wireless system available for mouse work. This has incidentally led to contributions in the areas of wireless power transfer and neural interfaces for upper-limb prosthesis control. Herein the solution space for wireless power transfer is examined including a close inspection of far-field power transfer to implanted bioelectric sensors. Methods of design and characterization for the iterative development of the device are detailed. Furthermore, its performance and utility in remote bioelectric sensing applications is demonstrated with humans, rats, healthy mice, and mouse models for degenerative neuromuscular and motoneuron diseases

Coupled resonator based wireless power transfer for bioelectronics

Implantable and wearable bioelectronics provide the ability to monitor and modulate physiological processes. They represent a promising set of technologies that can provide new treatment for patients or new tools for scientific discovery, such as in long-term studies involving small animals. As these technologies advance, two trends are clear, miniaturization and increased sophistication i.e. multiple channels, wireless bi-directional communication, and responsiveness (closed-loop devices). One primary challenge in realizing miniaturized and sophisticated bioelectronics is powering. Integration and development of wireless power transfer (WPT) technology, however, can overcome this challenge. In this dissertation, I propose the use of coupled resonator WPT for bioelectronics and present a new generalized analysis and optimization methodology, derived from complex microwave bandpass filter synthesis, for maximizing and controlling coupled resonator based WPT performance. This newly developed set of analysis and optimization methods enables system miniaturization while simultaneously achieving the necessary performance to safely power sophisticated bioelectronics. As an application example, a novel coil to coil based coupled resonator arrangement to wirelessly operate eight surface electromyography sensing devices wrapped circumferentially around an able-bodied arm is developed and demonstrated. In addition to standard coil to coil based systems, this dissertation also presents a new form of coupled resonator WPT system built of a large hollow metallic cavity resonator. By leveraging the analysis and optimization methods developed here, I present a new cavity resonator WPT system for long-term experiments involving small rodents for the first time. The cavity resonator based WPT arena exhibits a volume of 60.96 x 60.96 x 30.0 cm3. In comparison to prior state of the art, this cavity resonator system enables nearly continuous wireless operation of a miniature sophisticated device implanted in a freely behaving rodent within the largest space. Finally, I present preliminary work, providing the foundation for future studies, to demonstrate the feasibility of treating segments of the human body as a dielectric waveguide resonator. This creates another form of a coupled resonator system. Preliminary experiments demonstrated optimized coupled resonator wireless energy transfer into human tissue. The WPT performance achieved to an ultra-miniature sized receive coil (2 mm diameter) is presented. Indeed, optimized coupled resonator systems, broadened to include cavity resonator structures and human formed dielectric resonators, can enable the effective use of coupled resonator based WPT technology to power miniaturized and sophisticated bioelectronics

Wireless Technologies for Implantable Devices

Wireless technologies are incorporated in implantable devices since at least the 1950s. With remote data collection and control of implantable devices, these wireless technologies help researchers and clinicians to better understand diseases and to improve medical treatments. Today, wireless technologies are still more commonly used for research, with limited applications in a number of clinical implantable devices. Recent development and standardization of wireless technologies present a good opportunity for their wider use in other types of implantable devices, which will significantly improve the outcomes of many diseases or injuries. This review briefly describes some common wireless technologies and modern advancements, as well as their strengths and suitability for use in implantable medical devices. The applications of these wireless technologies in treatments of orthopedic and cardiovascular injuries and disorders are described. This review then concludes with a discussion on the technical challenges and potential solutions of implementing wireless technologies in implantable devices

Roadmap on semiconductor-cell biointerfaces.

This roadmap outlines the role semiconductor-based materials play in understanding the complex biophysical dynamics at multiple length scales, as well as the design and implementation of next-generation electronic, optoelectronic, and mechanical devices for biointerfaces. The roadmap emphasizes the advantages of semiconductor building blocks in interfacing, monitoring, and manipulating the activity of biological components, and discusses the possibility of using active semiconductor-cell interfaces for discovering new signaling processes in the biological world

Doctor of Philosophy

dissertationBy enabling neuroprosthetic technologies, neural microelectrodes can greatly improve diagnostic and treatment options for millions of individuals living with limb loss, paralysis, and sensory and autonomic neural disorders. However, clinical use of these devices is restricted by the limited functional lifetimes of implanted electrodes, which are commonly less than a few years. One cause is the evolution of damage to dielectric encapsulation that insulates microelectrodes from the physiological environment. Fluid penetration and exposure to an aggressive immunological response over time may weaken encapsulating films and cause electrical shunting. This reduces electrode impedance, diverts electrical signal away from target tissue, and causes multi-channel crosstalk. To date, no neural microelectrode encapsulating material or design approach has reliably resolved this issue. We employ the parylene C-encapsulated Utah Electrode Array (UEA), a silicon-micromachined neural interface FDA-cleared for human use, to execute three aims that address this challenge through investigations of new materials, electrode designs, and testing methods. We first evaluate a novel bilayer encapsulating film comprised of atomic layer deposited Al2O3 and parylene C, testing this film using UEAs and devices with UEA-relevant topography. Contrasting with previous work employing simplified planar structures, the incorporation of neural electrode features on test structures revealed failure modes pointing to the dissolution of Al2O3 over time. Our results emphasize the need for dielectric coatings resistant to water degradation as well as test methods that take electrode features into account. In our second aim, we show through finite element modeling and aggressive in vitro testing that use of degenerately doped silicon as a conductive neural electrode material can mitigate the consequences of encapsulation damage, owing to the high electrochemical impedance of silicon. Our final aim compares oxidative in vitro aging to long-term in vivo material damages and finds clear evidence that such in vitro testbeds may help predict certain in vivo damage modes. By pairing this testing with absorption and emission spectroscopic characterization modalities, we identify contributors to material damage and future design solutions. Our results will inform future material and testing choices, to improve the resilience of neural electrode dielectric encapsulation and enhance the longevity of neuroprostheses

Development of a novel intracortical electrode for chronic neural recordings

PhD ThesisMicromotion, attributable to the modulus mismatch between the brain and electrode materials, is a fundamental phenomenon contributing to electrode failure for invasive Brain-Machine Interfaces. Spike recording quality from conventional chronic electrode designs deteriorates over the weeks/months post-implantation, in terms of signal amplitude and single unit stability, due to glial cell activation by sustained mechanical trauma. Conventional electrode designs consist of a rigid straight shaft and sharp tip, which can augment mechanical trauma sustained due to micromotion. The sinusoidal probe has been fabricated to reduce micromotion related mechanical trauma. The electrode is microfabricated from flexible materials and has design measures such as a sinusoidal shaft, spheroid tip and a 3D polyimide ball anchor to restrict electrode movement relative to the surrounding brain tissue, thus theoretically minimising micromotion. The electrode was compared to standard microwire electrodes and was shown to have more stable chronic recordings in terms of SNR and LFP power. A longer chronic recording period was achieved with the sinusoidal probe for the first generation. Quantitative histology detecting microglia and astrocytes showed reduced neuronal tissue damage especially for the tip region between 6-24 months chronic indwelling period for the sinusoidal probe. This may be linked to the more stable chronic recordings. This is the first demonstration that electrode designs wholly incorporating micromotion- reducing measures may decrease the magnitude of gliosis, with possible chronic recording longevity enhancement

Encapsulated Magnetoelectric Composites for Wirelessly Powered Brain Implantable Devices

Magnetoelectric devices are readily employed as sensors, actuators, and antennas, but typically exhibit low power output. This paper presents considerations for the viability of magnetoelectric composites for wireless power transfer in neural implantation. This is accomplished herein by studying different types of biocompatible encapsulants for magnetoelectric devices, their impact on the output voltage of the composites, and the rigidity of the materials in the context of tissue damage. Simulation results indicate that a polymer encapsulant, rather than creating a substrate clamping effect, increases the voltage output of the magnetoelectric, which can be further improved by careful polymer selection. These attributes are modelled using the finite element method (FEM) with COMSOL Multiphysics. The addition of a 0.2 mm poly(ethyl acrylate) encapsulating layer increases the piezoelectric voltage to 3.77 V AC output at a magnetic field strength of 200 Oe, as the magnetostrictive layer deforms inside the flexible outer polymer. Comparing voltage conditioning circuits, the output is sufficient for low-voltage neuronal stimulation when employing a simple bridge rectifier which boasts minimal charging time and ripple voltage around 1 mV